Zebedee, I tend to agree with Catspaw.
You say you 'love her very much' yet you start this thread off with a posting that gives an impression that you have not really discovered what loving another person is all about. If you believe those words you wrote.... 'I expect that I will always feel this way, and unless I make a commitment one day, then I'll have a very lonely life', That to me is a pretty self-absorbed way of going about making a major decision to move in with someone you say you really do love very much.
Everyone needs time alone. If you both love each other, you will be sensitive to each other's need for space and time alone.
To me it sounds like you are going about this decision full of fear. Just be aware of that. To be fearful of a major decision like this, 'one foot in, one foot out', is not the best way to move in with someone who you feel you truly do love. Approaching this decision the way you appear to be approaching it may make you feel safe, but it will also limit the depth of intimacy you will be able to discover within your relationship with your girlfriend & yourself.

Little Neo